Multipathway Biomarker Profiling of Immunothrombosis in Moderate and Severe COVID-19

Background/Objectives: Coronavirus disease 2019 (COVID-19) is associated with immunothrombosis involving endothelial dysfunction and coagulation activation. We aimed to compare biomarkers spanning multiple immunothrombotic pathways between patients with moderate and severe COVID-19 at baseline and according to clinical outcome. Secondary analyses compared biomarker levels at days 3 and 7. Methods: This prospective observational study included 42 hospitalized patients with COVID-19 enrolled between April 2020 and January 2021, comprising 21 with moderate and 21 with severe disease. Biomarkers of coagulation, endothelial dysfunction, endogenous anticoagulant pathways, fibrinolysis, and extracellular vesicle-mediated activity were measured at baseline and on days 3 and 7. The prespecified ventilation/death composite included invasive mechanical ventilation already ongoing at baseline or initiated subsequently and/or death by day 28. Results: Seventeen patients (40.5%) met the composite criterion, including 12 patients already receiving invasive mechanical ventilation at baseline. At baseline, severe disease was associated with higher D-dimer (1.74 [0.87–3.67] vs. 0.68 [0.46–0.94] µg/mL FEU), free tissue factor pathway inhibitor (TFPI; 55.00 [38.00–109.00] vs. 16.00 [14.00–29.00] ng/mL), extracellular vesicle-associated tissue factor activity (EV-TF; 28.86 [13.61–48.72] vs. 5.00 [5.00–5.70] fM), and extracellular vesicle-associated plasmin generation capacity (EV-PGC; 93.36 [41.60–303.10] vs. 24.50 [16.14–35.74] fM; all p < 0.01). Exploratory ROC analyses further illustrated the separation of these biomarker distributions between the predefined clinical groups. Conclusions: Severe COVID-19 and unfavorable outcomes were associated with baseline differences in biomarkers spanning several immunothrombotic pathways, some of which remained detectable at days 3 and 7. Interpretation of the marked TFPI elevation is limited by differences in heparin exposure between severity groups. These exploratory findings require confirmation in larger cohorts, and their incremental value beyond routine clinical assessment remains untested. Outcome analyses largely reflected baseline severity, with only five subsequent events.